Interpretive Summary: The herbicide glyphosate is commonly used for weed management in citrus groves in Brazil. Some have suggested that sublethal exposure of citrus to this herbicide causes harmful effects. The most sensitive method of determination of whether glyphosate has a metabolic effect on plants an increase in shikimic acid level. Monitoring of shikimic acid content of citrus leaves for up to 35 days after two different typical sprayings of glyphosate for weed control revealed no significant effects on shikimic acid content. This suggests that, as typically used in citrus for weed management, glyphosate has no direct effects on citrus.

Technical Abstract:
This study was conducted to evaluate the effect of weed control with glyphosate on shikimic acid levels in citrus, “Pêra” cultivar. The experimental plots were set in Santo Antônio de Posse county, Sao Paulo State, Brazil with the following treatments: glyphosate at 1,440 g.ha-1 a.e. between citrus rows in 12/12/2006 and repeated 3.5 months later (04/02/2007) at rate of 1,260 g.ha-1 a.e., and control. Twenty Citrus leaves were then collected at zero, 03, 07, 10, 15, 20 and 35 days after treatment (DAT). Shikimic acid content was analyzed by HPLC after extraction assisted with microwave. The analytical method allowed recoveries varying from 89.74% to 100.76%. Results have shown no effect of glyphosate on shikimic acid content due to glyphosate treatments between areas during the period of study. Similar studes should be conducted in orchards in which glyphosate has been used for a long period of time.